Project III: Modulation of Biomarkers of Aflatoxin-exposure by Oltipraz. A major goal of public health practice is disease prevention. Recent advances in our understanding of the fundamental mechanisms of carcinogenesis have provided opportunities to reduce human cancer incidence through chemoprotective interventions. However, the use of cancer endpoints in the evaluation of new chemoprotective strategies ensures slow and costly progress. The development of intermediate biomarkers is essential to the timely maturation of the field of chemoprotection. The major objective of the work proposed in Project III is, through the use of animal modeling, to examine whether the biomarkers developed for assessing aflatoxin B1 exposure are also appropriate endpoints for assessing disease risk. We will thoroughly test the hypothesis that levels of biomarkers for the biologically effective dose of aflatoxin are predictive for assessing the efficacy of chemoprotective interventions in aflatoxin-exposed individuals. This hypothesis is based upon recent observations from our laboratory that an antischistosomal drug oltipraz dramatically reduces levels of the hepatic aflatoxin-DNA adducts and coordinately blocks aflatoxin-induced hepatocarcinogenesis in rats. Specifically, we will model in the rat the modulation of the levels of several biomarkers of aflatoxin exposure (including aflatoxin- N7-guanine in urine and aflatoxin-albumin adducts in serum) by a molecular intervention with oltipraz under dosing conditions that correspond to human exposure and intervention paradigms and to determine whether modulation of these biomarkers correlates with reduced risk for aflatoxin-induced toxicities. We will also probe the role of glutathione S-transferases in protecting against aflatoxin toxicities. Non-invasive methods will be developed to quantitate levels of aflatoxin-mercapturide in the urine and to determine the dose-response characteristics, if any, or urinary levels of this biomarker and tissue glutathione S-transferase activities following acute and chronic exposures to oltipraz and/or aflatoxin. In summary, the goal of this proposal is to characterize and validate biomarkers of aflatoxin exposure and to determine whether levels of these biomarkers can be modulated by a molecular intervention with oltipraz. Completion of these studies should establish a short-term, efficient means to evaluate oltipraz or other chemoprotective compounds as inhibitors of the acute and chronic effects of aflatoxin exposure in humans.